FAILED: patch "[PATCH] mm: memcg: fix NULL pointer in" failed to apply to 5.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Possible dependencies:

ac86f547ca10 ("mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath()")
203a31516616 ("mm/writeback: Add __folio_mark_dirty()")
9d8053fc7a21 ("mm/memcg: Convert mem_cgroup_track_foreign_dirty_slowpath() to folio")
a49d0c507759 ("mm/writeback: Add folio_wait_stable()")
490e016f229a ("mm/writeback: Add folio_wait_writeback()")
4268b48077e5 ("mm/filemap: Add folio_end_writeback()")
575ced1c8b0d ("mm/swap: Add folio_rotate_reclaimable()")
4e1364286d0a ("mm/filemap: Add folio_unlock()")
2f52578f9c64 ("mm/util: Add folio_mapping() and folio_file_mapping()")
3a6b2162005f ("mm: move page dirtying prototypes from mm.h")
6e1cae881a06 ("mm/writeback: move __set_page_dirty() to core mm")
34ebcce79324 ("fs: unexport __set_page_dirty")
87e378974975 ("mm/page-writeback: use __this_cpu_inc() in account_page_dirtied()")
9620ad86d0e3 ("afs: Re-enable freezing once a page fault is interrupted")
d479960e44f2 ("mm: disable LRU pagevec during the migration temporarily")
198fba4137a1 ("mm/mmzone.h: fix existing kernel-doc comments and link them to core-api")
a87132a22991 ("mm/doc: add mm.h and mm_types.h to the mm-api document")
842ca547f706 ("mm: move page_mapping_file to pagemap.h")
5cbf03985c67 ("afs: Use new netfs lib read helper API")
dc4191841d09 ("afs: Use the fs operation ops to handle FetchData completion")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ac86f547ca1002aec2ef66b9e64d03f45bbbfbb9 Mon Sep 17 00:00:00 2001
From: Kefeng Wang <wangkefeng.wang@huawei.com>
Date: Sun, 29 Jan 2023 12:09:45 +0800
Subject: [PATCH] mm: memcg: fix NULL pointer in
 mem_cgroup_track_foreign_dirty_slowpath()

As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"),
hwpoison will forcibly uncharg a LRU hwpoisoned page, the folio_memcg
could be NULl, then, mem_cgroup_track_foreign_dirty_slowpath() could
occurs a NULL pointer dereference, let's do not record the foreign
writebacks for folio memcg is null in mem_cgroup_track_foreign_dirty() to
fix it.

Link: https://lkml.kernel.org/r/20230129040945.180629-1-wangkefeng.wang@huawei.com
Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reported-by: Ma Wupeng <mawupeng1@huawei.com>
Tested-by: Miko Larsson <mikoxyzzz@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Ma Wupeng <mawupeng1@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d3c8203cab6c..85dc9b88ea37 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1666,10 +1666,13 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio,
 static inline void mem_cgroup_track_foreign_dirty(struct folio *folio,
 						  struct bdi_writeback *wb)
 {
+	struct mem_cgroup *memcg;
+
 	if (mem_cgroup_disabled())
 		return;
 
-	if (unlikely(&folio_memcg(folio)->css != wb->memcg_css))
+	memcg = folio_memcg(folio);
+	if (unlikely(memcg && &memcg->css != wb->memcg_css))
 		mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
 }